Wellbores are formed in subterranean formations for various purposes including, for example, the extraction of oil and gas from a subterranean formation and the extraction of geothermal heat from the subterranean formation. A wellbore may be formed in a subterranean formation using a drill bit, such as, an earth-boring rotary drill bit. Different types of earth-boring rotary drill bits are known in the art, including, for example, fixed-cutter bits (which are often referred to in the art as “drag” bits), including impregnated bits (having cutting structures impregnated with diamonds or other superabrasive particles), and hybrid bits (which may include, for example, both fixed cutters and rolling cutters, at least one of which may include one or more impregnated cutting structures).
The drill bit is coupled, either directly or indirectly, to an end of what is referred to in the art as a “drill string,” which comprises a series of elongated tubular segments connected end-to-end that extends into the wellbore from the surface of the formation. Often various tools and components, including the drill bit, may be coupled together at the distal end of the drill string at the bottom of the wellbore being drilled. This assembly of tools and components is referred to in the art as a “bottom hole assembly” (BHA).
The drill bit may be rotated within the wellbore by rotating the drill string from the surface of the earth using a rotary table or top drive, or the drill bit may be rotated by coupling the drill bit to a downhole motor, which is also coupled to the drill string and disposed proximate the bottom of the wellbore. In some instances, the drill string is simultaneously rotated from the surface and by a downhole motor. The downhole motor may comprise, for example, a hydraulic Moineau-type motor having a shaft, to which the drill bit is attached, that may be caused to rotate by pumping fluid (e.g., drilling mud or fluid) from the surface of the formation down through the center of the drill string, through the hydraulic motor, out from nozzles in the drill bit, and back up to the surface of the formation through the annular space between the outer surface of the drill string and the exposed surface of the formation within the wellbore.
Superabrasive-impregnated earth-boring rotary drill bits and other tools may be used for drilling hard or abrasive rock formations such as sandstones. Typically, a superabrasive-impregnated bit has a solid body, which is often referred to in the art as a “crown,” that is cast in a mold. The crown is attached to a steel shank having a threaded end that may be used to attach the crown and steel shank to a drill string. The crown may have a variety of configurations and generally includes a cutting face having a plurality of cutting structures, which may include at least one of cutting segments, posts, and/or blades. The posts and/or blades may be integrally formed with the crown in the mold, or they may be separately formed, as by a sintering or hot isostatic press (HIP) process, and attached to the crown. Channels extend between the posts and blades to allow drilling fluid to flow over the face of the bit and through the channels.
Superabrasive-impregnated drill bits may be formed such that the cutting face of the drill bit (including the segments, posts, blades, etc.) comprises a particle-matrix composite material that includes hard particles (e.g., superabrasive particles) dispersed throughout a matrix material and binder. The superabrasive particles may comprise natural or synthetic diamond or cubic boron nitride, the matrix material is conventionally cobalt-cemented tungsten carbide (WC—Co), and the binder may comprise copper.
While drilling with a superabrasive-impregnated bit, the matrix material and the binder surrounding the superabrasive particles wears at a faster rate than do the superabrasive particles. As the matrix material and binder surrounding the superabrasive particles on the surface of the bit wears away, the exposure of the superabrasive particles at the surface gradually increases until the superabrasive particles eventually fall away. As some superabrasive particles are falling away, others that were previously completely buried become exposed, such that fresh, sharp superabrasive particles are continuously being exposed and used to cut the earth formation.
A drill bit with integral impregnated posts is conventionally formed, in some instances, by mixing and distributing hard particles and matrix material powder (e.g., cemented tungsten carbide) in a mold cavity configured with an interior topography to receive same and define cutting structures. The particle mixture is then infiltrated with a molten metal binder material, such as a copper-based metal alloy. After infiltration, the molten metal matrix material is allowed to cool and solidify. The resulting drill bit including the integral impregnated posts may then be removed from the mold.
In other instances, an impregnated post is formed by forming a mixture including hard particles, a cemented carbide matrix material, and a binder in a hot isostatic press. The mixture is disposed in a press and pressed into a green body, which is then sintered by exposure to a hot isostatic pressing process wherein the green body is densified.